Knee braces are known. They typically include a thigh member for fastening to the thigh, a lower leg member for fastening to the lower leg and a hinge axis therebetween positioned over the knee to be reinforced. All manner of straps for securing the respective leg and thigh portions have been illustrated in the prior art.
1. Brief Description of the Relevant Art
The following prior art includes a representative sample of such prior art.
Some knee braces have included compound hinges. Such compound hinges include two or more pivot points closely spaced along the natural joint defined by the knee. Examples of such compound hinges include Lerman U.S. Pat. No. 4,372,298; Marquette U.S. Pat. No. 4,793,333; Kausek et al. 4,732,143; and European Patent Application 0173161 to Townsend.
A knee stabilizer is disclosed in Marquette U.S. Pat. No. 4,790,299 having a supracondylar support. This supracondylar support provides vertical location of the brace on the leg at the supracondylar hollow.
Many braces rely on a simple hinge axis rigidly braced with respect to the knee. Example of such devices include Ford U.S. Pat. No. 4,624,247; Martin et al. U.S. Pat. No. 4,503,846 and Myers et al. U.S. Pat. No. 4,802,466.
There is a known tendency of some knee braces to "piston" with respect to the leg. Such piston movement can be accommodated by various springs between the respective knee brace portions. Illustrative of such a spring arrangement is Carsalade British Patent Application 2,156,221.
2. Statement of the Problem
The knee, unlike the common hinge, has an asymmetrical hinging action. As the knee bends, the pivot point about which the bending occurs, changes. Reference to the views provided by FIGS. 6, 7, and 8 of this application can illustrate this point.
In FIGS. 6-8 a typical knee joint is illustrated in rotation. The outlines of femur E, tibia T and fibula F are illustrated within a normal leg having conventionally proportioned tissue. The knee is shown in rotation from an extended disposition as shown in FIG. 6 to a position approximately maximum flexion as shown in FIG. 8. Intermediate rotational positions are shown in FIG. 7.
Some reference to the skeletal anatomy of the knee is beneficial. The lower leg includes a fibula F and the tibia T. These bones have their upper surface jointly defining plateau K upon which the corresponding condyle of the femur turns. Applicable cartilage, ligaments, and muscle are, of course, omitted.
For reference in the following discussion, the tibia has been provided with center line 100. The reader will understand that as this discussion proceeds that the center of rotation of the condyle of the femur changes with respect to the center line during movement of the knee between the extended and flexed positions.
The femur E includes condyle C. Condyle C is not symmetrical with respect to the femur. This can be seen by inspecting FIGS. 6-8. As in the case of the tibia, the femur E has been given center line 102. This center line will also be used to discuss the asymmetry of the knee joint requiring the improvement of this invention.
Femur E normally rests upon the plateau K of the tibia at surface 9. However, upon flexion, resting occurs on surface 11 at plateau K. It is apparent at first glance that the illustrated "hinge action" of the knee is not symmetrical. This phenomenon can be further understood by referring to the respective "centers of rotation" of the condyle of the femur overlying the lower leg.
When the knee first begins to rotate from a position of extension to a position of flexion, turning of the joint of the knee first occurs about center 110. It can be seen that this center 110 is to the left of the center line 100 of the fibula tibia and also to the left of the center line 102 of the femur E.
When the knee finishes rotation to a point of near maximum flexion illustrated in FIG. 8, final turning occurs about center 120. It can be seen that this center in FIG. 7 has moved to the right of center line 100 of the fibula tibia.
Referring to FIG. 7, an attempt to trace the migration of the center of pivot with respect to the condyle K and the tibia is instructive. Specifically, the center of pivot moves along line 130 as the leg moves from extension deflection. This begins with the extension center of pivot 110 on the left and ends with the flexion center of pivot 120 on the right.
Once this diagram is seen and understood, the futility of providing a knee with a simple hinge for reinforcement of the knee can be clearly understood.
Assume that the full dynamic load is placed on the knee joint and the brace together during active body movement. As set forth in the prior art, assume that the brace holds a hinge axis as rigidly as possible at one rigid hinge axis location with respect to the knee joint. However, the knee, undergoing both flexion and extension will have its center of pivot moved with respect to the rigid hinge axis. As all those familiar with the simple concept of mechanics know, something relative to the knee with its moving center of pivot, the brace (or both) has to give in order to permit hinging axis. Indeed, a recitation of undesirable knee brace motions can catalog such conforming movements of the knee relative to a brace to permit the required hinge like movement of the knee joint.
Where the hinge axis of the brace is rigidly held with respect to the knee joint, a phenomenon commonly known a "pistoning" frequently occurs. Either the thigh portion or the lower leg portion (or both) move up and down with respect to the thigh or lower leg. Absent such movement, bending of the knee could not occur. Skin abrasions and flesh irritations are a common result of such "pistoning" movement.
This dynamic misalignment between the rigid hinge axis of a knee brace and the moving center of pivot of a knee also causes discomfort to the reinforced knee joint itself. As those familiar with mechanics know, two closely positioned but misaligned hinge axes acting on the same levers (the thigh and the lower leg) work against each other with considerable force. This considerable force can cause discomfort at the knee joint and even damage to the reinforced knee over a period of time.
Clearly there is a need to emulate in a knee brace, especially an activity knee brace, movement to the braced hinge axis which correspond in large measure to the movement of the knee center of rotation.
Daneman et al. U.S. Pat. No. 5,078,127 issued Jan. 7, 1992 entitled Knee Brace with Articulating Brace Hinge Axis constituted an attempt to approximate the movement of an activity brace with the dynamics of the human knee. In that disclosure, the combination of a offset condylar pad was combined with a knee brace to approximate the movement of the structural hinge axis to overlying the dynamically moving center of rotation of a knee joint during flexure and extension. What follows is a further attempt to obtain tracking between the dynamically changing center of pivot of a knee joint and the structural hinge member of an activity brace.